A common form of lifting tackle used on boats consists of a line run over a pulley (sometimes called a block or sheave). The line has a lifting end that is attached to the object being raised and a working end that is placed under tension to raise or secure the object at a position above the deck. The bight of the line is run over the pulley, and the pulley is fastened at a position above the location to which the object is to be raised (usually high above the deck near the top of the mast). The bight of the line is divided into two lengths separated at the point where it passes over the pulley. Namely, the bight has a lifting length, positioned between the pulley and the lifting end, and a working length positioned between the pulley and the deck.
When the object being raised is a sail or a flag, the line is called a halyard. Whenever the sail is raised to and secured in its desired location, the halyard is placed under tension and its working length is aligned in a predetermined halyard-under-tension direction.
A particularly serious problem can occur when a sailor is in the process of attaching the lifting end of the halyard to a sail or flag. Often, the sailor is holding the lifting end of the halyard several feet above the deck, while the working length of the halyard is extended from the pulley all the way down to the deck or, at least, to a location lower than the level at which the lifting end is being held. At this moment, the working length may be several feet longer than the lifting length, and it weighs more than the lifting length. If, at such a time, the lifting end of the halyard is lost from the sailor's grip, the difference between the relative weights of the two line lengths creates a moment which starts the pulley rotating in the direction of the heavier working length; and this rotational force very rapidly increases as the free lifting end moves upward and becomes continuously lighter relative to the weight of the working length. Therefore, unless the sailor is able to quickly regain a grip on the lifting end, the halyard will runaway, running fully off the pulley or, if it is knotted to a shackle, leaving the lifting end jammed in the pulley high above the deck.
It should be noted that this problem is quite different from the more common problem experienced with such tackle. That is, whenever a halyard is under load, there is always the danger that the sailor's grip may be lost on the working length. For instance, when raising a jib sail, the wind may suddenly fill the sail, wrenching the halyard out of the sailor's hand. To secure the working end of the line, or to prevent its being dragged through the pulley by the sail or other load being raised by the lifting end, the working end is usually passed around a fixed cleat or pulled through a tension-activated or hand-activated cam-action cleat or stopper. Such activated belaying mechanisms have an increasingly narrowing passageway (usually provided with saw-tooth like surfaces) that close around the line with a grip that increases in direct proportion to the tension of the load being raised or secured.
There are many known variations of hand- or tension-activated cam-cleat type stoppers designed for lifting tackle to prevent the working end of the line from running away under load. One such known line-locker, which is specifically designed for anchor line tackle, grips the working length of the anchor line between the deck and one end of a pivoted clamping bar in the event (a) tension is released on the working end of the line and (b) the line begins to run out under the weight of the anchor. In this anchor line stopper, the working length of the line is subjected to adjacent reverse bends by being passed over two adjacent rope guides, one of which is secured to the deck and the other to the clamping bar; and the clamping bar, which is biased toward its clamping position by gravity, is pulled down toward the deck so that it clamps down on the line with a force proportional to the tension exerted on the lifting length by the weight of the anchor.
As just stated above, these known halyard stops and clamps are directed to the problem of securing the working end of the line when the lifting end is under tension. They are not directed to, nor can they be used to solve, the problem solved by my invention, namely, the problem of a runaway halyard caused by a loss of tension on the lifting length of the tackle.